Question

Un con circular drept are aria totala de 36 pi si generatoare de 9 cm. Aflati raza.
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Answer 1

Explicație pas cu pas:

At=Al+Ab

At=36π cm²

At=πrg+πr²

36π=π*r*9+π*r² |:π

36=9r+r²

r²+9r-36=0

r²+12r-3r-36=0

r(r+12)-3(r+12)=0

(r-3)(r+12)=0

r=3 ( cm )

Bafta!

Answer 2

$\it \mathcal{A}_{t} = \mathcal{A}_{b}+ \mathcal{A}_{\ell}=\pi R^2+\pi RG=\pi R(R+G)\ \ \ \ \ (1)\\ \\ \\ \mathcal{A}_{t}=36\pi cm^2,\ iar\ G=9\ cm\ \ \ \ \ (2)\\ \\ \\ (1),\ (2) \Rightarrow \pi R(R+9) =36\pi|_{:\pi} \Rightarrow R(R+9)=36 \Rightarrow R=3\ cm$